Abstract
AbstractVegetation covers on dikes and embankment dams have proven as sustainable and cost‐effective surface protection against external erosion caused by hydraulic, mechanical, or climatic impacts. Determination of the hydraulic loads that act upon these covers requires the knowledge of the flow resistance. While the high‐velocity flows on vegetated slopes are often aerated, the flow aeration has rarely been considered, and no direct measurements of the air‐water flow properties have been conducted to date. The air‐water flow properties are needed for a direct estimation of important design parameters such as friction factors and residual head at the downstream end. Herein, unique air‐water flow measurements were conducted in high‐velocity air‐water flows down a vegetated chute with a 1:3 slope. Several vegetation covers were tested for a range of flow rates. The experiments revealed strong flow aeration within three‐dimensional, fragmented flows associated with complex interactions of vegetation and high‐velocity flows. The air‐water flow properties were measured with phase‐detection intrusive probes providing novel insights into aerated flows on vegetated chutes including distributions of void fraction, bubble count rate, and interfacial velocity as well as direct estimates of energy dissipation and flow resistance. The results highlighted strong flow aeration and energy dissipation for all vegetated configurations. The median equivalent Darcy‐Weisbach friction factors for all vegetations were within 0.19 to 0.45, comparable to aerated flows on stepped spillways. The present results highlighted the significant flow resistance of vegetated covers and the need to consider air‐water flow properties in the design of vegetated chutes.
Highlights
Natural and nature‐based solutions in the water resources field have drawn attention due to opportunities of, for example, increasing biodiversity, provision of habitats, regulating services, such as carbon sequestration or water purification, and the offer of cultural services
Extensive research on flow resistance in supercritical, aerated flows has been conducted in nonvegetated hydraulic conveyance structures with typical embankment dam slopes, such as smooth spillways (Anderson, 1965; Cain & Wood, 1981; Felder & Severi, 2016; Straub & Anderson, 1960; Wood, 1983), stepped spillways (e.g., Felder & Chanson, 2015c; Hunt et al, 2014), gabion stepped spillways (Wüthrich & Chanson, 2014), and rock chutes (Pagliara et al, 2010)
Full‐scale model tests on a smooth and five vegetated chutes with θ = 18.4° were conducted for a range of stationary discharges qw ≤ 0.215 m2/s to investigate the flow aeration and flow resistance of high‐velocity aerated flows on vegetated chutes
Summary
Natural and nature‐based solutions in the water resources field have drawn attention due to opportunities of, for example, increasing biodiversity, provision of habitats, regulating services, such as carbon sequestration or water purification, and the offer of cultural services. Extensive research on flow resistance in supercritical, aerated flows has been conducted in nonvegetated hydraulic conveyance structures with typical embankment dam slopes, such as smooth spillways (Anderson, 1965; Cain & Wood, 1981; Felder & Severi, 2016; Straub & Anderson, 1960; Wood, 1983), stepped spillways (e.g., Felder & Chanson, 2015c; Hunt et al, 2014), gabion stepped spillways (Wüthrich & Chanson, 2014), and rock chutes (Pagliara et al, 2010) These and many further studies used phase‐detection intrusive probes to measure the air‐water flow properties and to estimate the design parameters including flow resistance and energy dissipation performance. The results provided novel insights into flow aeration, energy dissipation performances, and flow resistance in high‐velocity supercritical flows down vegetated chutes with submerged vegetation
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